Reduced transistor bridge attenuator

ABSTRACT

An apparatus includes a bypass circuit a resistor circuit and multiple staggered circuits. The bypass circuit may have a predetermined number of a plurality of transistors connected in series between an input node and an output node. The resistor circuit may have a given number of resistors connected in series between the input node and the output node. Adjoining pairs of the resistors may be connected at given nodes. The staggered circuits may be connected between the given nodes and either the input node or the output node. Each staggered circuit may have a respective number of the transistors connected in series. The bypass circuit, the resistor circuit and the staggered circuits may form part of a bridge attenuator.

This application relates to U.S. Provisional Application No. 62/580,029,filed Nov. 1, 2017, which is hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The invention relates to attenuator circuits generally and, moreparticularly, to a method and/or apparatus for implementing a reducedtransistor bridge attenuator.

BACKGROUND

Bridge attenuators are used to control an attenuation of a signal.Conventional bridge attenuator designs connect field effect transistorsin series along parallel paths between an input node and an output nodeto achieve varying levels of attenuation. A common number of transistorsare used in each path. The common number is selected such that a maximumvoltage between the input node and the output node does not cause adrain-to-source breakdown of the transistors in any of the paths. Aproblem with the conventional designs is that a large number oftransistors are used to implement the bridge attenuators.

It would be desirable to implement a reduced transistor bridgeattenuator.

SUMMARY

The invention concerns an apparatus including a bypass circuit aresistor circuit and multiple staggered circuits. The bypass circuit mayhave a predetermined number of a plurality of transistors connected inseries between an input node and an output node. The resistor circuitmay have a given number of resistors connected in series between theinput node and the output node. Adjoining pairs of the resistors may beconnected at given nodes. The staggered circuits may be connectedbetween the given nodes and either the input node or the output node.Each staggered circuit may have a respective number of the transistorsconnected in series. The bypass circuit, the resistor circuit and thestaggered circuits may form part of a bridge attenuator.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will be apparent from the followingdetailed description and the appended claims and drawings in which:

FIG. 1 is a block diagram illustrating an apparatus in accordance withan example embodiment of the invention;

FIG. 2 is a block diagram illustrating an attenuator in the apparatus inaccordance with an example embodiment of the invention;

FIG. 3 is a schematic diagram illustrating a bridge circuit in theattenuator in accordance with an example embodiment of the invention;

FIG. 4 is schematic diagram illustrating a shunt circuit in theattenuator in accordance with an example embodiment of the invention;

FIG. 5 is a schematic diagram illustrating another bridge circuit inaccordance with an example embodiment of the invention;

FIG. 6 is a schematic diagram illustrating yet another bridge circuit inaccordance with an example embodiment of the invention;

FIG. 7 is a schematic diagram illustrating still another bridge circuitin accordance with an example embodiment of the invention;

FIG. 8 is a schematic diagram illustrating another shunt circuit inaccordance with an example embodiment of the invention;

FIG. 9 is a schematic diagram illustrating still another shunt circuitin accordance with an example embodiment of the invention;

FIG. 10 is a diagram illustrating another attenuator in accordance withan example embodiment of the invention; and

FIG. 11 is a diagram illustrating relative channel sizes of multipletransistors in accordance with an example embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention include providing a reducedtransistor bridge attenuator that may (i) be implemented with fewertransistors than conventional designs, (ii) form part of a fifthgeneration (5G) wireless communications system, (iii) operate withdrain-to-source breakdown voltages less than a maximum signal voltage,(iv) occupy less area than conventional designs and/or (v) beimplemented as one or more integrated circuits.

Embodiments of the present invention generally provide a bridgeattenuator circuit having fewer switching transistors than in commondesigns. The transistor count may be reduced by using a staggeredarchitecture in the bridge arms (e.g., staggered bridges) to reduce themaximum voltage swing seen by each respective bridge arm. Since some ofthe bridge arms experience a reduced maximum voltage, such bridge armsmay be implemented with fewer switching transistors.

Referring to FIG. 1, a block diagram illustrating an apparatus 90 isshown in accordance with an example embodiment of the invention. Theapparatus (or device or system or circuit) 90 may implement an amplifierwith variable levels of amplification and/or attenuation. The apparatus90 generally comprises a block (or circuit) 92, a block (or circuit) 94,a ground node 96 and a block (or circuit) 100.

A signal (e.g., IN) may be received by the block 92. The signal IN mayimplement an input signal to be amplified/attenuated over apredetermined range. In some embodiments, the signal IN may be aradio-frequency signal. The signal IN may be used in a fifth generation(5G) wireless communications system, a fourth generation (4G) wirelesscommunications system (International Mobile Telecommunications Advancedstandard) or a long range wireless communications system. A signal(e.g., AMP) may be generated by the circuit 92 and received by thecircuit 100. The signal AMP may be an amplified version of the signalIN. The circuit 100 may receive a signal (e.g., CTR). The signal CTR maybe a control signal used to control a level of attenuation. In variousembodiments, the signal CTR may contain multiple independent components(or independent control signals). A signal (e.g., OUT) may be generatedby the circuit 100 and transferred to the circuit 94. The output signalOUT may implement a variable version of the signal AMP. In somesituations, the signal OUT may be the same as the signal AMP. In othersituations the signal OUT may be an attenuated version of the signalAMP.

The circuit 92 may implement an amplifier circuit. The amplifier 92 isgenerally operational to amplify the signal IN to generate the signalAMP. In some embodiments, the amplification may be a fixed amplification(e.g., +20 decibels (dB)). In other embodiments, the amplification maybe a variable amplification. Other levels of amplification may beimplemented to meet the design criteria of a particular application.

The circuit 94 may implement a load impedance (or circuit). The loadimpedance 94 may be operational to receive the signal OUT. In variousembodiments, the load impedance 94 may be a resistive load, an inductiveload, a capacitive load, or a combination of resistance, inductanceand/or capacitance to the signal ground node 96.

The circuit 100 may implement a variable attenuation circuit. Theattenuation circuit 100 may be operational to attenuate the signal AMPto generate the signal OUT. The level of attenuation may be controlledby the individual components of the signal CTR. In some embodiments, theattenuation level may vary from approximately 0 dB to approximately −30dB. Other levels of attenuation may be implemented to meet the designcriteria of a particular application. In various embodiments, theattenuation circuit 100 may implement a staggered attenuation circuithaving fewer transistors than in common designs.

Referring to FIG. 2, a block diagram illustrating an exampleimplementation of the attenuator 100 is shown in accordance with anexample embodiment of the invention. The attenuator 100 generallycomprises a block (or circuit) 102 and a block (or circuit) 104. Thesignal AMP may be received by the circuit 102. The signal OUT may begenerated and presented by the circuit 102. The circuit CTR may bereceived by both the circuit 102 and the circuit 104. The circuit 104may be connected to the signal ground node 96. A signal (e.g., INT) maybe exchanged between the circuit 102 and the circuit 104. The signal INTmay be an intermediate signal that conveys part of the signal AMP to thesignal ground node 96.

The circuit 102 may implement a bridge circuit. The bridge circuit 102is generally operational to attenuate the signal AMP to generate thesignal OUT. The degree of attenuation may be determined by the signalCTR. In some situations, part of the power received in the signal AMPmay be dissipated by the circuitry within the bridge circuit 102. In thevarious situations, part of the power received in the signal AMP may bepassed to the circuit 104 in the signal INT. In a bypass situation, allof the power received in the signal AMP may be transferred to the signalOUT.

The circuit 104 may implement a shunt circuit. The shunt circuit 104 isgenerally operational to present a variable impedance between the bridgecircuit 102 and the signal ground node 96. The variable impedance may bedetermined by the signal CTR. Referring to FIG. 3, a schematic diagramillustrating an example implementation of the bridge circuit 100 isshown in accordance with an example embodiment of the invention. Thebridge circuit 100 generally comprises an input node 106, an output node108, a block (or circuit) 110, a block (or circuit) 112, a block (orcircuit) 114, one or more blocks (or circuits) 116 (one shown forsimplicity) and a block (or circuit) 118.

The signal AMP may be received at the input node 106. The input node 106may be connected to all of the circuit 110, the circuit 116 and thecircuit 118. The signal OUT may be presented from the output node 108.The output node 108 may be connected to all of the circuit 110, thecircuit 112, the circuit 114, the circuit 116 and the circuit 118. Thesignal INT may be connected to an intermediate node 120 within thecircuit 118. The signal CTR may comprise multiple control signals (orcomponents) (e.g., CTRA to CTRC). The signal CTRA may be received by thecircuit 110. The signal CTRB may be received by the circuit 112. Thesignal CTRC may be received by the circuit 114.

The circuit 110 may implement a bypass bridge circuit (or bypass circuitfor short). The bypass circuit 110 is generally operational to provideeither an open circuit or a closed circuit between the input node 106and the output node 108 as controlled by the signal CTRA. While thesignal CTRA is asserted, the bypass circuit 110 may present a closedstate (or condition) between the input node 106 and the output node 108.While the signal CTRA is deasserted, the bypass circuit 110 may presentan open state (or condition) between the input node 106 and the outputnode 108.

The bypass circuit 110 generally comprises multiple transistors (e.g., Jtransistors) connected in series. In various embodiments, eachtransistor may be implemented as a field effect transistor. Thetransistors within the bypass circuit 110 may be wired in series witheach other. A gate of each transistor may receive the signal CTRA toswitch the transistors between a conducting condition (e.g., the closedstate) and a non-conducting condition (e.g., the open state).

The number of transistors in the bypass circuit 110 is generallydetermined by (i) a maximum voltage swing between the input node 106 andthe output node 108 and (ii) a minimum drain-to-source breakdown voltageof each transistor. Consider a case where the minimum drain-to-sourcebreakdown voltage of each transistor is BV_(DS) volts and the maximumvoltage swing between the input node 106 and the output node 108 (e.g.,at maximum attenuation of the signal AMP) is V_(MAX) volts. Byimplementing J transistors in the bypass circuit 110, the maximumvoltage seen by each transistor will not exceed BV_(DS) volts ifJxBV_(DS)>V_(MAX).

Each circuit 112 and 114 may implement a staggered bridge circuit (orstaggered circuit for short). The staggered circuits 112 and 114 aregenerally operational to provide either the open circuit or the closedcircuit between a respective node in the circuit 116 and the output node108 as controlled by the respective signals CTRB and CTRC. While thesignal CTRB is asserted, the staggered circuit 112 may present theclosed state (or condition) between an intermediate node 122 within thecircuit 116 and the output node 108. While the signal CTRB isdeasserted, the staggered circuit 112 may present the open state (orcondition) between the intermediate node 122 within the circuit 116 andthe output node 108. While the signal CTRC is asserted, the staggeredcircuit 114 may present the closed state (or condition) between anotherintermediate node 124 within the circuit 116 and the output node 108.While the signal CTRC is deasserted, the staggered circuit 114 maypresent the open state (or condition) between the other intermediatenode 124 within the circuit 116 and the output node 108. In variousembodiments, additional stagger circuits may be added between respectivenodes in the circuit 116 and the output node 108. The additional staggercircuits may be controlled by additional components of the signal CTR.

The staggered circuit 112 generally comprises multiple transistors(e.g., K transistors). In various embodiments, each transistor may beimplemented as a field effect transistor. The transistors within thestaggered circuit 112 may be the same type of transistor(s) as withinthe bypass circuit 110. The transistors within the staggered circuit 112may be wired in series with each other. A gate of each transistor mayreceive the signal CTRB to switch the transistors between the conductingcondition (e.g., the closed state) and the non-conducting condition(e.g., the open state).

The number of transistors in the staggered circuit 112 is generallydetermined by (i) a maximum voltage swing between the intermediate node122 in the circuit 116 and the output node 108, (ii) a minimumdrain-to-source breakdown voltage of each transistor and (iii) a voltagedrop from the input node 106 to the intermediate node 122 (e.g., avoltage drop across the resistor RA). In designs where the voltage dropacross the resistor RA is greater than the breakdown voltage BV_(DS),the number K of transistors in the stagger circuit 112 may be fewer thanthe number J of transistors in the bypass circuit 110 (e.g., K<J).

The staggered circuit 114 generally comprises multiple transistors(e.g., L transistors). In various embodiments, each transistor may beimplemented as a field effect transistor. The transistors within thestaggered circuit 114 may be the same type of transistor(s) as withinthe bypass circuit 110 and/or the staggered circuit 112. The transistorswithin the staggered circuit 114 may be wired in series with each other.A gate of each transistor may receive the signal CTRC to switch thetransistors between the conducting condition (e.g., the closed state)and the non-conducting condition (e.g., the open state). In variousembodiments, the staggered circuit 114 may have fewer numbers oftransistors than the staggered circuit 112. The staggered circuit 114generally has fewer numbers of the transistors than the bypass circuit110.

The number of transistors in the staggered circuit 114 is generallydetermined by (i) a maximum voltage swing between an intermediate node124 in the circuit 116 and the output node 108, (ii) a minimumdrain-to-source breakdown voltage of each transistor and (iii) a voltagedrop from the input node 106 to the intermediate node 124 (e.g., avoltage drop across the resistors RA and RB). In designs where thevoltage drop across the resistors RA and RB is greater than thebreakdown voltage BV_(DS), the number L of transistors in the staggercircuit 114 may be fewer than the number K of transistors in the staggercircuit 112 (e.g., L<K). As a result, the total number of transistors inthe bridge circuit 102 (e.g., J+K+L) may be fewer than the number oftransistors in a common bridge circuit (e.g., J+J+J) with the samenumber of active bridges between the input node 106 and the output node108. By utilizing fewer transistors, the bridge circuit 102 may occupy asmaller area than common bridge circuits.

The circuit 116 may implement a resistor bridge circuit (or resistorcircuit for short). The resistor circuit 116 is generally operational toprovide a series resistance between the input node 106 and the outputnode 108. The resistor circuit 116 generally comprises multipleresistors RA to RC. The resistors RA to RC may be wired to each other inseries. Each junction of two (or an adjoining pair) of the resistors RAto RC may form the intermediate nodes 122 and 124. Each intermediatenode 122 and 124 within the resistor circuit 116 may be connected to anend of the staggered circuits 112 and 114 opposite the output node 108.Generally, the resistor circuit 116 may have at least one more resistorthan the number of staggered circuits. In the example, three resistorsRA to RC are shown. In various embodiments, more than three resistorsmay be implemented to meet the design criteria of a particularapplication.

The circuit 118 may implement another resistor bridge circuit (orresistor circuit for short). The resistor circuit 118 generallycomprises two or more resistors (e.g., RD to RE). The resistors RD to REmay be wired together in series. The intermediate node 120 may beestablished between two of the resistors (e.g., between the resistor RDand the resistor RE). The intermediate node 120 may be connected to theshunt circuit 104 and carry the signal INT.

Consider an example involving just the bridge circuit 100 where (i) theminimum drain-to-source breakdown voltage BV_(DS) of each transistor is3 volts, (ii) the maximum voltage swing of the signal AMP is 16 voltsand (iii) the resistor RB=2xRA and RC=3xRA (e.g., a total resistance ofthe circuit 116 is 6xRA). While the bridge circuit 100 is in a bypassmode (e.g., no attenuation), the signal CTRA may be asserted and all ofthe transistors in the bypass circuit 110 are in the closed state. Assuch, the signal OUT generally tracks the signal AMP and the voltagedifference between the input node 106 and the output node 108 isessentially zero volts (ignoring the voltage drop across theclosed-state transistors). The voltage difference between theintermediate node 122 and the output node 108 is zero volts. Likewise,the voltage difference between the intermediate node 124 and the outputnode 108 is zero volts.

When the bridge circuit 100 is set at a maximum attenuation level (e.g.,all of signals CTRA, CTRB and CTRC are deasserted), the signal OUT maybe at a fraction (e.g., ⅛th in the example) of the signal AMP. Themaximum voltage difference between the input node 106 and the outputnode 108 may thus be approximately (16 volts-2 volts=) 14 volts. Sincethe bypass circuit 110 is subject to the full 14 volt difference, fivetransistors may be included in the bypass circuit 110 such thatdrain-to-source voltage across each transistor (e.g., 14 volts/5transistors=2.8 volts/transistor) is less than the breakdown voltageBV_(DS) of 3 volts.

The voltage across the staggered circuit 112 may be the voltage acrossthe resistors RB and RC. In the example, the voltage across theresistors RB and RC may be approximately (5/6×14 volts=) 11.7 volts.Therefore, the staggered circuit 112 may be implemented with fourtransistors such that drain-to-source voltage across each transistor(e.g., 11.7 volts/4 transistors=2.9 volts/transistor) is less than thebreakdown voltage BV_(DS) of 3 volts. In a common design, the staggeredcircuit 112 would span from the input node 106 to the output node 108,would experience the full 14 volt difference, and so would beimplemented with 5 transistors.

The voltage across the open-state staggered circuit 114 may be thevoltage across the resistor RC. In the example, the voltage across theresistor RC may be approximately (3/6×14 volts=) 7 volts. Therefore, thestaggered circuit 114 may be implemented with three transistors suchthat drain-to-source voltage across each transistor (e.g., 7 volts/3transistors=2.3 volts/transistor) is less than the breakdown voltageBV_(DS) of 3 volts. In a common design, the staggered circuit 114 wouldspan from the input node 106 to the output node 108, would experiencethe full 14 volt difference, and so would be implemented with 5transistors. As such, the invention may be implemented with fewer (e.g.,5+4+3=12) transistors than the number of transistors (e.g., 5+5+5=15) ina common design. Utilizing fewer transistors may allow the invention tooccupy a smaller circuit area than common designs.

Referring to FIG. 4, a schematic diagram illustrating an exampleimplementation of the shunt circuit 104 is shown in accordance with anexample embodiment of the invention. The shunt circuit 104 generallycomprises a block (or circuit) 130, a block (or circuit) 132, a block(or circuit) 134, an intermediate node 136 and multiple resistors (e.g.,RF to RH). The intermediate node 136 of the shunt circuit 104 may beconnected to the intermediate node 120 of the bridge circuit 102. Invarious embodiments, the intermediate node 136 and the intermediate node120 may be the same node. The resistors RF, RG and RH may all beconnected to the intermediate node 136. The signal INT may be receivedby the circuits 130, 132 and 134 through the respective resistors RF, RGand RH. Each circuit 130, 132 and 134 may have an end connected to thesignal ground node 96. The circuit 130 may receive a signal (e.g.,CTRD). The circuit 132 may receive a signal (e.g., CRTE). The circuit134 may receive a signal (e.g., CRTF). Each signal CTRD, CTRE and CTRFmay be a component of the control signal CTR.

Each circuit 130-134 may implement a shunt arm circuit (or arm circuitfor short). The arm circuits 130-134 may be operational to provideeither the open circuit condition or the closed circuit conditionbetween the respective resistors RF to RH and the signal ground node 96.The open/closed conditions may be controlled by the respective signalsCTRD, CTRE and CTRF.

Each arm circuit 130-134 may include multiple transistors (e.g., S, Tand U transistors respectively). The transistors in each arm circuit130-134 may be wired together in series. In various embodiments, eachtransistor may be a field effect transistor. The transistors within eacharm circuit 130-134 may be the same type of transistor(s) as thetransistors in the bridge circuit 102. In various embodiments, thenumber of transistors S in the arm circuit 130 may be the same as thenumber of transistors T in the arm circuit 132 and the number oftransistors U in the arm circuit 134 (e.g., S=T=U).

A gate of each transistor in the arm circuit 130 may be controlled bythe signal CTRD. While the signal CTRD is asserted, the arm circuit 130may present the closed state (or condition) between the resistor RF andthe signal ground node 96. While the signal CTRD is deasserted, the armcircuit 130 may present the open state (or condition) between theresistor RF and the signal ground node 96. While the signal CTRE isasserted, the arm circuit 132 may present the closed state (orcondition) between the resistor RG and the signal ground node 96. Whilethe signal CTRE is deasserted, the arm circuit 132 may present the openstate (or condition) between the resistor RG and the signal ground node96. While the signal CTRF is asserted, the arm circuit 134 may presentthe closed state (or condition) between the resistor RH and the signalground node 96. While the signal CTRF is deasserted, the arm circuit 134may present the open state (or condition) between the resistor RH andthe signal ground node 96. In various embodiments, additional resistorsand additional arm circuits may be added between the intermediate node136 and the signal ground node 96. The additional resistors and armcircuits may be controlled by additional components of the signal CTR.

Referring to FIG. 5, a schematic diagram illustrating an exampleimplementation of a bridge circuit 102 a is shown in accordance with anexample embodiment of the invention. The bridge circuit 102 a may be avariation of the bridge circuit 102. The bridge circuit 102 a may beconnected to the amplifier 92, the load impedance 94 and the arm circuit104 the same way as the bridge circuit 102.

The bridge circuit 102 a generally comprises the bypass circuit 110, ablock (or circuit) 112 a, a block (or circuit) 114 a, a block (orcircuit) 116 a and the resistor circuit 118. The signal AMP may bereceived by the bypass circuit 110, the circuit 112 a, the circuit 114a, the circuit 116 a and the resistor circuit 118. The signal OUT may becreated by the bypass circuit 110, the circuit 116 a and the circuit118. The signal INT may be presented from the node 120 within theresistor circuit 118. The signal CTRA may be received by the bypasscircuit 110. The signal CTRB may be received by the circuit 112 a. Thesignal CTRC may be received by the circuit 114 a.

Each circuit 112 a and 114 a may implement a staggered bridge circuit(or staggered circuit for short). The staggered circuits 112 a and 114 aare generally operational to provide either the open circuit or theclosed circuit between respective nodes 122 and 124 in the circuit 116 aand the input node 106 as controlled by the respective signals CTRB andCTRC. While the signal CTRB is asserted, the staggered circuit 112 a maypresent the closed state (or condition) between the input node 106 andthe intermediate node 122 within the circuit 116 a. While the signalCTRB is deasserted, the staggered circuit 112 a may present the openstate (or condition) between the input node 106 and the intermediatenode 122 within the circuit 116 a. While the signal CTRC is asserted,the staggered circuit 114 a may present the closed state (or condition)between the input node 106 and the intermediate node 124 within thecircuit 116 a. While the signal CTRC is deasserted, the staggeredcircuit 114 may present the open state (or condition) between the inputnode 106 and the intermediate node 124 within the circuit 116 a. Invarious embodiments, additional stagger circuits may be added betweenthe input node 106 and the respective nodes in the circuit 116 a. Theadditional stagger circuits may be controlled by additional componentsof the signal CTR.

The staggered circuit 112 a generally comprises multiple transistors(e.g., K transistors). In various embodiments, each transistor may beimplemented as a field effect transistor. The transistors within thestaggered circuit 112 a may be the same type of transistor(s) as withinthe bypass circuit 110. The transistors within the staggered circuit 112a may be wired in series with each other. A gate of each transistor mayreceive the signal CTRB to switch the transistors between the conductingcondition (e.g., the closed state) and the non-conducting condition(e.g., the open state).

The number of transistors in the staggered circuit 112 a is generallydetermined by (i) a maximum voltage swing between the intermediate node122 in the circuit 116 a and the input node 106, (ii) a minimumdrain-to-source breakdown voltage of each transistor and (iii) a voltagedrop from the output node 108 to the respective node 122 (e.g., avoltage drop across the resistor RA). In designs where the voltage dropacross the resistor RA is greater than the breakdown voltage BV_(DS),the number K of transistors in the stagger circuit 112 a may be fewerthan the number J of transistors in the bypass circuit 110 (e.g., K<J).

The staggered circuit 114 a generally comprises multiple transistors(e.g., L transistors). In various embodiments, each transistor may beimplemented as a field effect transistor. The transistors within thestaggered circuit 114 a may be the same type of transistor(s) as withinthe bypass circuit 110 and/or the staggered circuit 112 a. Thetransistors within the staggered circuit 114 a may be wired in serieswith each other. A gate of each transistor may receive the signal CTRCto switch the transistors between the conducting condition (e.g., theclosed state) and the non-conducting condition (e.g., the open state).In various embodiments, the staggered circuit 114 a may have fewertransistors than the staggered circuit 112 a. The staggered circuit 114a generally has fewer transistors than the bypass circuit 110.

The number of transistors in the staggered circuit 114 a is generallydetermined by (i) a maximum voltage swing between the intermediate node124 in the circuit 116 a and the input node 106, (ii) a minimumdrain-to-source breakdown voltage of each transistor and (iii) a voltagedrop from the output node 108 to the respective node 124 (e.g., avoltage drop across the resistors RA and RB). In designs where thevoltage drop across the resistors RA and RB is greater than thebreakdown voltage BV_(DS), the number L of transistors in the staggercircuit 114 a may be fewer than the number K of transistors in thestagger circuit 112 a (e.g., L<K). As a result, the total number oftransistors in the bridge circuit 102 a (e.g., J+K+L) may be fewer thanthe number of transistors in a common bridge circuit (e.g., J+J+J) withthe same number of active bridges between the input node 106 and theoutput node 108. The fewer number of transistors in the bridge circuit102 a may occupy a smaller area than in common bridge circuits.

The circuit 116 a may implement a resistor bridge circuit (or resistorcircuit for short). The resistor circuit 116 a is generally operationalto provide a series resistance between the input node 106 and the outputnode 108. The resistor circuit 116 a generally comprises multipleresistors RA to RC. The resistors RA to RC may be wired to each other inseries. The resistor circuit 116 a may be a variation of the resistorcircuit 116 with the order of the resistors RA to RC and the order ofthe nodes 122 to 124 reversed between the input node 106 and the outputnode 108. In the example, three resistors RA to RC are shown. In variousembodiments, more than three resistors may be implemented to meet thedesign criteria of a particular application.

Referring to FIG. 6, a schematic diagram illustrating an exampleimplementation of a bridge circuit 102 b is shown in accordance with anexample embodiment of the invention. The bridge circuit 102 b may be avariation of the bridge circuits 102 and/or 102 a. The bridge circuit102 b may be connected to the amplifier 92, the load impedance 94 andthe shunt circuit 104 the same way as the bridge circuits 102 and 102 a.In various embodiments, the bridge circuit 102 b may have at least twoamong the bypass circuit and/or the stagger circuits having a samenumber of transistors.

The bridge circuit 102 b generally comprises the bypass circuit 110, ablock (or circuit) 112 b, the stagger circuit 114, the resistor circuit116 and the resistor circuit 118. The signal AMP may be received by thebypass circuit 110, the resistor circuit 116 and the resistor circuit118. The signal OUT may be created by the bypass circuit 110, thecircuit 112 b, the stagger circuit 114, the resistor circuit 116 and theresistor circuit 118. The signal INT may be presented from a node withinthe resistor circuit 118. The signal CTRA may be received by the bypasscircuit 110. The signal CTRB may be received by the circuit 112 b. Thesignal CTRC may be received by the stagger circuit 114 a.

The circuit 112 b may implement a staggered bridge circuit (or staggeredcircuit for short). The staggered circuit 112 b is generally operationalto provide either the open circuit or the closed circuit between thenode 122 in the resistor circuit 116 and the output node 108 ascontrolled by the signal CTRB. While the signal CTRB is asserted, thestaggered circuit 112 b may present the closed state (or condition)between the node 122 and the output node 108. While the signal CTRB isdeasserted, the staggered circuit 112 b may present the open state (orcondition) between the node 122 and the output node 108.

The staggered circuit 112 b generally comprises multiple transistors(e.g., K transistors). In various embodiments, each transistor may beimplemented as a field effect transistor. The transistors within thestaggered circuit 112 b may be the same type of transistor(s) as withinthe bypass circuit 110. The transistors within the staggered circuit 112b may be wired in series with each other. A gate of each transistor mayreceive the signal CTRB to switch the transistors between the conductingcondition (e.g., the closed state) and the non-conducting condition(e.g., the open state).

The number of transistors in the staggered circuit 112 b is generallydetermined by (i) a maximum voltage swing between the intermediate node122 in the resistor circuit 116 and the output node 108, (ii) a minimumdrain-to-source breakdown voltage of each transistor and (iii) a voltagedrop from the input node 106 to the node 122 (e.g., a voltage dropacross the resistor RA). In various designs (e.g., where the voltagedrop across the resistor RA is less than the breakdown voltage BV_(DS)),the number (e.g., K) of transistors in the stagger circuit 112 b maymatch the number of transistors than the bypass circuit 110 (e.g., J=K).The number of transistors in the stagger circuit 112 b and the bypasscircuit 110 may still be greater than the number of transistors in thestagger circuit 114 (e.g., J=K>L). In various embodiments, additionalstagger circuits with the same number of transistors as the bypasscircuit 110 and the stagger circuit 112 b may be added between therespective nodes within the resistor circuit 116 and the output node108. The additional stagger circuits may be controlled by additionalcomponents of the signal CTR.

Referring to FIG. 7, a schematic diagram illustrating an exampleimplementation of a bridge circuit 102 c is shown in accordance with anexample embodiment of the invention. The bridge circuit 102 c may be avariation of the bridge circuits 102, 102 a and/or 102 b. The bridgecircuit 102 c may be connected to the amplifier 92, the load impedance94 and the shunt circuit 104 the same way as the bridge circuits 102,102 a and 102 b. In various embodiments, the bridge circuit 102 c mayhave the same number of transistors in all of the bypass circuit and/orthe stagger circuits.

The bridge circuit 102 c generally comprises the bypass circuit 110, thestagger circuit 112 b, a block (or circuit) 114 b, the resistor circuit116 and the resistor circuit 118. The signal AMP may be received by thebypass circuit 110, the resistor circuit 116 and the resistor circuit118. The signal OUT may be created by the bypass circuit 110, thestagger circuit 112 b, the circuit 114 b, the resistor circuit 116 andthe resistor circuit 118. The signal INT may be presented from the node120 within the resistor circuit 118. The signal CTRA may be received bythe bypass circuit 110. The signal CTRB may be received by the staggercircuit 112 b. The signal CTRC may be received by the circuit 114 a.

The circuit 114 b may implement a staggered bridge circuit (or staggeredcircuit for short). The staggered circuit 114 b is generally operationalto provide either the open circuit or the closed circuit between thenode 124 in the resistor circuit 116 and the output node 108 ascontrolled by the signal CTRC. While the signal CTRC is asserted, thestaggered circuit 114 b may present the closed state (or condition)between the node 124 and the output node 108. While the signal CTRC isdeasserted, the staggered circuit 114 b may present the open state (orcondition) between the node 124 and the output node 108.

The staggered circuit 114 b generally comprises multiple transistors(e.g., L transistors). In various embodiments, each transistor may beimplemented as a field effect transistor. The transistors within thestaggered circuit 114 b may be the same type of transistor(s) as withinthe bypass circuit 110. The transistors within the staggered circuit 114b may be wired in series with each other. A gate of each transistor mayreceive the signal CTRC to switch the transistors between the conductingcondition (e.g., the closed state) and the non-conducting condition(e.g., the open state).

The number of transistors in the staggered circuit 114 b is generallydetermined by (i) a maximum voltage swing between the intermediate node124 in the resistor circuit 116 and the output node 108, (ii) a minimumdrain-to-source breakdown voltage of each transistor and (iii) a voltagedrop from the input node 106 to the node 124 (e.g., a voltage dropacross the resistors RA and RB). In various designs (e.g., where thevoltage drop across the resistors RA and RB is less than the breakdownvoltage BV_(DS)), the number (e.g., L) of transistors in the staggercircuit 114 b may match the number of transistors than the bypasscircuit 110 and the stagger circuit 114 b (e.g., J=K=L). In variousembodiments, additional stagger circuits with the same number oftransistors as the bypass circuit 110 and the stagger circuit 112 b maybe added between the respective nodes within the resistor circuit 116and the output node 108. The additional stagger circuits may becontrolled by additional components of the signal CTR.

Referring to FIG. 8, a schematic diagram illustrating an exampleimplementation of a shunt circuit 104 a is shown in accordance with anexample embodiment of the invention. The shunt circuit 104 a may be avariation of the shunt circuit 104. The shut circuit 104 a may beconnected to the bridge circuits 102, 102 a and/or 102 b the same way asthe shunt circuit 104. In various embodiments, the shunt circuit 104 amay have at least one arm circuit with a different number of transistorsthan the other arm circuits.

The shunt circuit 104 a generally comprises a block (or circuit) 130 a,the arm circuit 132, the arm circuit 134 and the resistors RF-RH. Theintermediate node 136 of the shunt circuit 104 a may be connected to theintermediate node 120 of a bridge circuit 102/102 a/102 b to receive thesignal INT. The intermediate node 136 may be connected through theresistors RF-RH to respective ends of the circuits 130 a-134. The otherends of the circuits 130 a-134 may be connected to the signal groundnode 96.

The circuit 130 a may implement a shunt arm circuit (or arm circuit forshort). The arm circuit 130 a may be operational to provide either theopen circuit condition or the closed circuit condition between theresistors RF and the signal ground node 96. The open/closed conditionsmay be controlled by the signals CTRD.

The arm circuit 130 a may include multiple transistors (e.g., Stransistors). The transistors in the circuit 130 a may be wired togetherin series. In various embodiments, each transistor may be a field effecttransistor. The transistors within the arm circuit 130 a may be the sametype of transistor(s) as the transistors in the bridge circuits 102-102b. In various embodiments, the number of transistors S in the armcircuit 130 a may be different than the number of transistors T in thearm circuit 132 and the number of transistors U in the arm circuit 134(e.g., S>T=U or S<T=U).

A gate of each transistor in the arm circuit 130 a may be controlled bythe signal CTRD. While the signal CTRD is asserted, the arm circuit 130a may present the closed state (or condition) between the resistor RFand the signal ground node 96. While the signal CTRD is deasserted, thearm circuit 130 a may present the open state (or condition) between theresistor RF and the signal ground node 96. In various embodiments,additional resistors and additional arm circuits may be added betweenthe intermediate node 136 and the signal ground node 96. The additionalarm circuits may have the same number of transistors as (i) the armcircuit 130 a or (ii) the arm circuits 132-134. The additional armcircuits may be controlled by additional components of the signal CTR.

Referring to FIG. 9, a schematic diagram illustrating an exampleimplementation of a shunt circuit 104 b is shown in accordance with anexample embodiment of the invention. The shunt circuit 104 b may be avariation of the shunt circuits 104 and/or 104 a. The shut circuit 104 bmay be connected to the bridge circuits 102, 102 a and/or 102 b the sameway as the shunt circuits 104-104 a. In various embodiments, the shuntcircuit 104 b may have different numbers of transistors in all of thearm circuits.

The shunt circuit 104 b generally comprises the arm circuit 130 a, ablock (or circuit) 132 a, the arm circuit 134 and the resistors RF-RH.The intermediate node 136 of the shunt circuit 104 b may be connected tothe intermediate node 120 of a bridge circuit 102/102 a/102 b to receivethe signal INT. The intermediate node 136 may be connected through theresistors RF-RH to respective ends of the circuits 130 a-134. The otherends of the circuits 130 a-134 may be connected to the signal groundnode 96. The circuit 132 a may implement a shunt arm circuit (or armcircuit for short). The arm circuit 132 a may be operational to provideeither the open circuit condition or the closed circuit conditionbetween the resistors RG and the signal ground node 96. The open/closedconditions may be controlled by the signals CTRE. The arm circuit 132 amay include multiple transistors (e.g., T transistors). The transistorsin the circuit 132 a may be wired together in series. In variousembodiments, each transistor may be a field effect transistor. Thetransistors within the arm circuit 132 a may be the same type oftransistor(s) as the transistors in the bridge circuits 102-102 b. Invarious embodiments, the number of transistors T in the arm circuit 132a may be different from the number of transistors S in the arm circuit130 a (e.g., ST). The number of transistors T in the arm circuit 132 amay also be different from the number of transistors U in the armcircuit 134 (e.g., TU).

A gate of each transistor in the arm circuit 132 a may be controlled bythe signal CTRE. While the signal CTRE is asserted, the arm circuit 132a may present the closed state (or condition) between the resistor RFand the signal ground node 96. While the signal CTRE is deasserted, thearm circuit 132 a may present the open state (or condition) between theresistor RG and the signal ground node 96. In various embodiments,additional resistors and additional arm circuits may be added betweenthe intermediate node 136 and the signal ground node 96. The additionalarm circuits may have different numbers of transistors as the armcircuits 130 a, 132 a and 134. The additional arm circuits may becontrolled by additional components of the signal CTR.

Referring to FIG. 10, a diagram illustrating an example implementationof another attenuator 100 a is shown in accordance with an exampleembodiment of the invention. The attenuator 100 a may be a variation ofthe attenuator 100. The attenuator 100 a generally comprises the bypasscircuit 110, multiple blocks (or circuits) 115 a-115 m, multiple blocks(or circuits) 138 a-138 n, multiple resistors R1A-R1N, the resistors RDand RE, and multiple resistors R2A-R2N.

The signal AMP may be received at the input node 106. The input node 106may be connected to all of the circuit 110, the circuit 116 and thecircuit 118. The signal OUT may be presented from the output node 108.The output node 108 may be connected to all of the circuit 110, thecircuits 115 a-115 m, the circuit 116 and the circuit 118. The signalINT may be connected to an intermediate node 120 within the circuit 118.The signal CTR may comprise multiple control signals (or components)(e.g., CTRA and CTR1A-CTR1M). The signal CTRA may be received by thecircuit 110. The signals CTR1A-CTR1M may be received by the respectivecircuits 115 a-115 m.

The intermediate node 136 may be connected to the intermediate node 120to convey the signal INT. In various embodiments, the intermediate node136 and the intermediate node 120 may be the same node. The resistorsR2A-R2N may all be connected to the intermediate node 136. The signalINT may be received by the circuits 138 a-138 n through the respectiveresistors R2A-R2N. Each circuit 138 a-138 n may have an end connected tothe signal ground node 96. The signal CTR may further comprise multiplecontrol signals (or components) (e.g., CTR2A-CTR2N). The circuits 138a-138 n may receive the signals CTR2A-CTR2N, respectively.

Each circuit 115 a-115 m may implement a staggered bridge circuit (orstaggered circuit for short). The staggered circuits 115 a-115 m aregenerally operational to provide either the open circuit or the closedcircuit between respective nodes in the circuit 116 and the output node108 as controlled by the respective signals CTR1A to CRT1M. While anindividual signal CTR1A-CTR1M is asserted, the respective staggeredcircuit 115 a-115 m may present the closed state (or condition) betweenrespective intermediate node within the circuit 116 and the output node108. While an individual signal CTR1A-CTR1M is deasserted, therespective staggered circuit 115 a-115 m may present the open state (orcondition) between the corresponding intermediate node within thecircuit 116 and the output node 108.

Each staggered circuit 115 a-115 m generally comprises multipletransistors. In various embodiments, each transistor may be implementedas a field effect transistor. The transistors within the staggeredcircuits 115 a-115 m may be the same type of transistor(s) as within thebypass circuit 110. The transistors within the staggered circuits 115a-115 m may be wired in series with each other. A gate of eachtransistor may receive a corresponding signal CTR1A-CTR1M to switch thetransistors between the conducting condition (e.g., the closed state)and the non-conducting condition (e.g., the open state). In variousembodiments, additional stagger circuits may be added between respectivenodes in the circuit 116 and the output node 108. The additional staggercircuits may be controlled by additional components of the signal CTR.

Each circuit 138 a-138 n may implement a shunt arm circuit (or armcircuit for short). The arm circuits 138 a-138 n may be operational toprovide either the open circuit condition or the closed circuitcondition between the respective resistors R2A-R2N and the signal groundnode 96. The open/closed conditions may be controlled by the respectivesignals CTR2A-CTR2N.

Each arm circuit 138 a-138 n may include multiple transistors. Thetransistors in each arm circuit 138 a-138 n may be wired together inseries. In various embodiments, each transistor may be a field effecttransistor. The transistors within each arm circuit 138 a-138 n may bethe same type of transistor(s) as the transistors in the bypass circuit110.

A gate of each transistor in the arm circuits 138 a-138 n may becontrolled by the corresponding signals CTR2A-CTR2N. While a signalCTR2A-CTR2N is asserted, the corresponding arm circuit 138 a-138 n maypresent the closed state (or condition) between the correspondingresistor R2A-R2N and the signal ground node 96. While a signalCTR2A-CTR2N is deasserted, the corresponding arm circuit 138 a-138 n maypresent the open state (or condition) between the corresponding resistorR2A-R2N and the signal ground node 96. In various embodiments,additional resistors and additional arm circuits may be added betweenthe intermediate node 136 and the signal ground node 96. The additionalresistors and the additional arm circuits may be controlled byadditional components of the signal CTR.

Referring to FIG. 11, a diagram illustrating relative channel sizes inexample implementations of multiple transistors 140-142 is shown inaccordance with an example embodiment of the invention. Each transistor140-142 may be implemented as a field effect transistor. Various mixesof the transistors 140-142 may be used to implement the bridge circuits102-102 b and the shunt circuits 104-104 b. Each transistor 140-142generally comprises a gate (G) node, a source (S) node and a drain (D)node.

The transistor 140 may implement a large transistor. The transistor 140may have a channel width (or periphery width) WA and a channel lengthLA. In various embodiments, the channel width WA may range fromapproximately 2.4 millimeters (mm) to approximately 3.6 mm. The channellength LA may be approximately 190 nanometers (nm) to approximately 290nm. Other channel widths and/or channel lengths may be implemented tomeet the design criteria of a particular application.

The transistor 142 may implement a medium transistor. The transistor 142may have a channel width (or periphery width) WB and a channel lengthLB. The channel width WB of the transistor 142 is generally smaller thanthat channel width WA of the transistor 140. The smaller channel widthWB may result in the transistor 142 having a higher impedance than thetransistor 140 while both are in a conducting (or closed) state. In somecases, the channel length LB of the transistor 142 may be shorter thanthe channel length LA of the transistor 140. In various embodiments, thechannel width WB may range from approximately 0.9 mm to approximately1.5 mm. The channel length LB may be approximately 190 nm to 290 nm.Other channel widths and/or channel lengths may be implemented to meetthe design criteria of a particular application.

The transistor 144 may implement a small transistor. The transistor 144may have a channel width (or periphery width) WC and a channel lengthLC. The channel width WC of the transistor 144 is generally smaller thanthat channel width WB of the transistor 142. The smaller channel widthWC may result in the transistor 144 having a higher impedance than thetransistor 142 while both are in a conducting (or closed) state. In somecases, the channel length LC of the transistor 144 may be shorter thanthe channel length LB of the transistor 142. In various embodiments, thechannel width WC may range from approximately 0.9 mm to approximately1.5 mm. The channel length LB may be approximately 78 nm to 290 nm.Other channel widths and/or channel lengths may be implemented to meetthe design criteria of a particular application.

A respective conducting mode (e.g., closed state) impedance of eachbypass circuit 110, each staggered circuit 112-112 b, 114-114 b and 115a-115 m and each arm circuit 130-130 a, 132-132 a, 134 and 138 a-138 nmay be determined by a total number of transistors used to implement thecircuits 110-138 n. The respective conducting mode impedance of thecircuits 110-138 n may be increased by increasing the number oftransistors implemented within the circuits.

The respective conducting mode impedance of each bypass circuit 110,each staggered circuit 112-112 b, 114-114 b and 115 a-115 m and each armcircuit 130-130 a, 132-132 a, 134 and 138 a-138 n may also be determinedby the size of the transistors 140-144 used to implement the circuits110-138 n. The respective conducting mode impedance of the circuits110-138 n may be increased by using the medium transistors 142 in placeof the large transistors 140, using the small transistors 144 in placeof the medium transistors 142 and/or using the small transistors 144 inplace of the large transistors 140.

A total impedance though each bridge of the bridge circuits 102-102 band/or each arm of the shunt circuits 104-104 b may be adjusted byimplementing different numbers of transistors in the circuits 110-138 n,different sizes of the transistors in the circuits 110-138 n and/ordifferent resistances in the resistors RA-R2N. For example, while thesignals CTRA and CTRB in the off state and the signal CTRC in the onstate, the impedance of the bridge circuit 102 (FIG. 3) between the node124 and the output node 108 may be controlled by a design of theconductive impedance through the stagger circuit 114 in parallel withthe resistance of the resistor RC. The total impedance of the parallelpaths from the node 124 to the output node 108 may be increased by (i)increasing a number of transistors in the stagger circuit 114, (ii)decreasing a size of the transistors in the stagger circuit 114, (iii)increasing the resistance of the resistor RC or (iv) any combinationthereof. The number of transistors and the size of the transistors usedin a particular implementation generally depends on maximum powerlevels, intended impedances and maximum voltages experienced by theattenuator 100.

While FIGS. 3 and 5-7 show the various bypass circuits 110 and thestagger circuits 112-112 b and 114-114 b implemented with three to fivetransistors each, other numbers of transistors may be implemented tomeet the design criteria of a particular application. In variousembodiments, each circuit 110, 112, 114 and 115 a-115 m may beimplemented with 12-16 transistors (e.g., 14, and 14 transistorsrespectively for three stagger circuit designs). The different sizedtransistors 140-142 may be used in the circuits 110-115 m (e.g., large,medium and small transistors respectively) to establish the conductingmode impedances. Other combinations of transistor numbers and/ortransistor sizes may be implemented to meet the design criteria of aparticular application.

While FIGS. 4, 8 and 9 show the various arm circuits 130-130 b, 132-132b and 134 implemented with three to five transistors each, other numbersof transistors may be implemented to meet the design criteria of aparticular application. In some designs, each circuit 130, 132, 134 and138 a-138 n may be implemented with 22 to 31 transistors (e.g., 24, 29and 29 transistors respectively in three arm circuit designs). Thedifferent sized transistors 140-142 may be used in the circuits 130-138n to establish the conducting mode impedances (e.g., large, medium andsmall respectively). Other combinations of transistor numbers and/ortransistor sizes may be implemented to meet the design criteria of aparticular application.

The functions and structures illustrated in the diagrams of FIGS. 1 to11 may be designed, modeled, emulated, and/or simulated using one ormore of a conventional general purpose processor, digital computer,microprocessor, microcontroller, distributed computer resources and/orsimilar computational machines, programmed according to the teachings ofthe present specification, as will be apparent to those skilled in therelevant art(s). Appropriate software, firmware, coding, routines,instructions, opcodes, microcode, and/or program modules may readily beprepared by skilled programmers based on the teachings of the presentdisclosure, as will also be apparent to those skilled in the relevantart(s). The software is generally embodied in a medium or several media,for example non-transitory storage media, and may be executed by one ormore of the processors sequentially or in parallel.

Embodiments of the present invention may also be implemented in one ormore of ASICs (application specific integrated circuits), FPGAs (fieldprogrammable gate arrays), PLDs (programmable logic devices), CPLDs(complex programmable logic device), sea-of-gates, ASSPs (applicationspecific standard products), and integrated circuits. The circuitry maybe implemented based on one or more hardware description languages.Embodiments of the present invention may be utilized in connection withflash memory, nonvolatile memory, random access memory, read-onlymemory, magnetic disks, floppy disks, optical disks such as DVDs and DVDRAM, magneto-optical disks and/or distributed storage systems.

The terms “may” and “generally” when used herein in conjunction with“is(are)” and verbs are meant to communicate the intention that thedescription is exemplary and believed to be broad enough to encompassboth the specific examples presented in the disclosure as well asalternative examples that could be derived based on the disclosure. Theterms “may” and “generally” as used herein should not be construed tonecessarily imply the desirability or possibility of omitting acorresponding element.

While the invention has been particularly shown and described withreference to embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made withoutdeparting from the scope of the invention.

1. An apparatus comprising: a bypass circuit having a predeterminednumber of a plurality of transistors connected in series between aninput node and an output node; a resistor circuit having a given numberof a plurality of resistors connected in series between said input nodeand said output node, wherein adjoining pairs of said resistors areconnected at a plurality of given nodes; and a plurality of staggeredcircuits connected between said given nodes and either said input nodeor said output node, wherein (i) each of said staggered circuits has arespective number of said transistors connected in series and (ii) saidbypass circuit, said resistor circuit and said staggered circuits formpart of a bridge attenuator.
 2. The apparatus according to claim 1,wherein each of said stagger circuits has fewer of said transistors thansaid bypass circuit.
 3. The apparatus according to claim 1, wherein atleast one of said staggered circuits has fewer of said transistors thananother of said staggered circuits.
 4. The apparatus according to claim1, wherein said bypass circuit and each of said staggered circuits havea same number of said transistors.
 5. The apparatus according to claim1, wherein said transistors in each of said bypass circuit and saidstaggered circuits are controlled between an open state and a closedstate by a respective one of a plurality of control signals.
 6. Theapparatus according to claim 1, wherein a sum of a plurality ofdrain-to-source breakdown voltages of said transistors in said staggeredcircuits is less than a maximum voltage swing between said input nodeand said output node.
 7. The apparatus according to claim 1, furthercomprising an additional resistor circuit having (i) an additionalnumber of said resistors connected in series between said input node andsaid output node and (ii) an intermediate node connected between two ofsaid resistors in said additional resistor circuit.
 8. The apparatusaccording to claim 7, further comprising a plurality of shunt armcircuits connected in parallel and configured to vary an impedancebetween said intermediate node to a ground node.
 9. The apparatusaccording to claim 1, wherein said transistors in said bypass circuitoccupy more area than said transistors in said staggered circuits. 10.The apparatus according to claim 1, wherein said transistors in one ofsaid staggered circuits occupy more area than said transistors inanother of said staggered circuits.
 11. An apparatus comprising: a shuntcircuit configured to vary an impedance between an intermediate node anda ground node in response to a control signal; and a bridge circuit (i)connected to said intermediate node, an input node and an output nodeand (ii) configured to generate an output signal by attenuating an inputsignal in response to said control signal, wherein (a) said bridgecircuit includes (i) a bypass circuit having a predetermined number of aplurality of transistors connected in series (ii) a resistor circuithaving a given number of a plurality of resistors connected in series ata plurality of given nodes and (iii) a plurality of staggered circuitsconnected between said given nodes and either said input node or saidoutput node and (b) each of said staggered circuits has a respectivenumber of said transistors connected in series.
 12. The apparatusaccording to claim 11, wherein each of said stagger circuits has fewerof said transistors than said bypass circuit.
 13. The apparatusaccording to claim 11, wherein at least one of said staggered circuitshas fewer of said transistors than another of said staggered circuits.14. The apparatus according to claim 11, wherein said bypass circuit andeach of said staggered circuits have a same number of said transistors.15. The apparatus according to claim 11, wherein said transistors ineach of said bypass circuit and said staggered circuits are controlledbetween an open state and a closed state by a respective one of aplurality of components of said control signal.
 16. The apparatusaccording to claim 11, wherein a sum of a plurality of drain-to-sourcebreakdown voltages of said transistors in said staggered circuits isless than a maximum voltage swing between said input node and saidoutput node.
 17. The apparatus according to claim 11, wherein saidbridge circuit further includes an additional resistor circuit having(i) an additional number of said resistors connected in series betweensaid input node and said output node and (ii) said intermediate node isconnected between two of said resistors in said additional resistorcircuit.
 18. The apparatus according to claim 11, wherein saidtransistors in said bypass circuit occupy more area than saidtransistors in said staggered circuits.
 19. The apparatus according toclaim 11, wherein said transistors in one of said staggered circuitsoccupy more area than said transistors in another of said staggeredcircuits.